:I rechecked the stringer for level along its length and across its width ... both are good. I made height measurements with and without a jig (built to the manufacturers setup specs) and both approaches verify the setup of the stringer. My conclusion is that there are small imperfection on the underside of the tub where it sits on the stringer. I'm inclined to use Henry 547 underlayment as filler for the small gap between the stringer and the bottom of the tub flange. A few experimental pieces I made seemed to work out OK. If anyone has a better idea (a structural foam?) I'm open to suggestions.

Paul B.e-plumber : It's dead-on! I've triple checked it along the length of the tub!

: Reply:: Confirn the level width wise as well, this is just as crucial as the level length wise. If the stringer wasn't placed exactly where it is required to be according to manufacturer specs, this could be the problem. The bathub itself could also have a slight imperfection on the underside where it sits on the stringer.: e-plumber

: : : It may be dead level, parallel, and smooth, but is it at the exact height so that it is supporting the flange but not lifting the tub off the floor?

: : : : I have installed an Americast Princeton bathtub and find that flex under load at the back wall stringer creates a creaking noise. I confirmed the tub to be level front to back and side to side. The flange of the tub has a small gap (1/6 to 3/32 of an inch) at the drain end when resting on the stringer and the flex noise in that area stops when a small cedar wedge is fitted. I cannot find any other point with a tub flange to stringer gap of any sort.

: : : : I have removed the tub inspected the stringer and floor and found them to be dead level, parallel and smooth.

: : : : In preparation for reinstallation, I sanded off the mold selvage along the underside of the tubs flange area but am wondering whether there is any sort of bedding that I might put on the stringer to eliminate gaps and the resultant creaking noise when loaded? I'm concerned that whatever I do needs to be able to support the roughly 700 pound of water that a full tub will hold and have reasonable longevity.

: : : : Given the large number of these tubs sold I can't believe I'm the only one experiencing this problem.